1. Field of the Invention
The present invention relates to a method for forming a resist under layer film used for a fine patterning in a manufacturing step of a semiconductor device, etc., and a patterning process using same.
2. Description of the Related Art
As an exposure light to be used for formation of a resist pattern, light exposure using a g-beam (436 nm) or an i-beam (365 nm) of a mercury lamp has widely been used in 1980's. As a means for further miniaturization, a method of shifting to a shorter wavelength of exposure light has been considered to be effective, so that in a mass-production process after a DRAM (dynamic random access memory) with 64 MB (processing dimension is 0.25 μm or less) in 1990's, a KrF excimer laser (248 nm) at a shorter wavelength was used as an exposure light source instead of the i-beam (365 nm). However, in production of DRAMs at integration degrees of 256 MB and 1 GB or higher which require a finer processing technique (processing dimension is 0.2 μm or less), light sources at a shorter wavelength were required, thereby a photolithography using an ArF excimer laser (193 nm) has been earnestly investigated in the past ten years. At first, the ArF lithography was intended to be firstly applied to a device fabrication of a 180 nm node device, but the KrF excimer lithography was prolonged in life to a mass-production of a 130 nm node device, so that the ArF lithography was firstly and fully applied to a 90 nm node. Further, such a technique was combined with a lens having an NA increased to 0.9, thereby conducting a mass-production of a 65 nm node device. For the next 45 nm node device, further shortening of a wavelength of the exposure light was progressing, and the F2 lithography with a wavelength of 157 nm was considered to be a candidate. However, development of the F2 lithography has stopped due to various problems such as an increased cost of a scanner since an expensive CaF2 single crystal is used for a projection lens with a large amount, an optical system shall be changed accompanying with introduction of a hard pellicle instead of a soft pellicle having extremely low durability, etching resistance of the resist film is lowered, etc., whereby an ArF liquid immersion lithography has been introduced.
In the ArF liquid immersion lithography, such water having a refractive index of 1.44 was introduced between a projection lens and a wafer by a partial filling manner, thereby enabling a high-speed scanning to conduct mass-production of a 45 nm node device by means of a lens having an NA of about 1.3.
As a candidate of lithography technique for a 32 nm node, vacuum ultraviolet light (EUV) lithography with a wavelength of 13.5 nm has been mentioned. As problems of the EUV lithography, there may be mentioned a laser to be increased in output, a resist film to be increased in higher sensitivity, a resolution to be enhanced, a line edge roughness (LER) to be lowered, an MoSi laminated mask to be free of defects, reflective mirror aberrations to be lowered, etc., whereby the problems to be overcome are piled up. The development of the high refractive index liquid immersion lithography which is another candidate as a technique for a 32 nm node has stopped since the LUAG, a candidate of a high refractive index lens, exhibits a lower transmittance, and it has been impossible to obtain a liquid having a refractive index increased to a targeted value of 1.8. Thus, in the light exposure used as a general-purpose technique, it is approaching the essential limit of the resolution derived from the wavelength of the light sources.
Thus, as one of the miniaturization techniques attracted attention in recent years, there is a double patterning process which forms a pattern by the first time exposure and development, and forms a pattern by the second time exposure at just between the patterns of the first time (Non-Patent Document 1). As the method of the double patterning, many processes have been proposed. For example, (1) it may be mentioned a method in which a photoresist pattern with a distance of the line and the space of 1:3 is formed by the first time exposure and development, the hard mask of the under layer is processed by the dry etching, a hard mask is further provided thereon with another layer, a line pattern is formed at the first time exposure space portion by exposure and development of the photoresist film, the hard mask is processed by dry etching to form a line and space pattern with a half pitch of the initial pattern. Also, (2) a photoresist pattern with a distance of the space and the line of 1:3 is formed by the first time exposure and development, a hard mask which is an under layer is processed by dry etching, a photoresist film is coated thereon, a space pattern of the second time is exposed to the portion at which the hard mask is remained, and the hard mask is processed by dry etching. Here, in the method (1), the hard mask must be prepared twice, while in the method (2), formation of the hard mask is performed once, but a trench pattern shall be formed, which is difficult to resolve as compared with the line pattern. Also, in both of the methods, the procedures for processing the hard mask by dry etching are performed twice.
As the other miniaturization techniques, there has been proposed a method in which a line pattern in the X-direction is formed on the positive type resist film using a dipole illumination, the resist pattern is cured, a resist material is again coated thereon, a line pattern in the Y-direction is exposed by a dipole illumination, whereby a hole pattern is formed from gaps of the latticed line pattern (Non-Patent Document 2).
As one of the methods for transferring a lithography pattern to a substrate by utilizing the hard mask, there is a multi-layer resist method. The multi-layer resist method comprises interposing an under layer film, e.g., a silicon-containing resist under layer film, having different etching selectivity from that of a photoresist film, i.e., a resist upper layer film between the resist upper layer film and a substrate to be processed, after obtaining a pattern onto the resist upper layer film, the pattern thus obtained is transferred onto the resist under layer film by dry etching using the resist upper layer film pattern as an etching mask, and further, the pattern thus obtained is transferred onto the substrate to be processed by dry etching using the resist under layer film pattern as an etching mask.
In addition, as mentioned above, finer substrate processing has recently been more complex. Specifically, it is increasingly important to flatten unevenness on a substrate using a resist under layer film in order to reduce a change in thickness of a resist intermediate film and a resist upper layer film formed thereon. This flattening process can enlarge focus margin of lithography to obtain a favorable process margin. Under the circumstances, a method for forming a resist under layer film having excellent filling/flattening properties is strongly demanded so that unevenness on a substrate can be flattened even in complex processes such as a multi-layer resist method and a double patterning.